This invention generally relates to a method and apparatus for controlling step motor operation and, more particularly, to a method and apparatus for simultaneously controlling a multiplicity of step motors having individual operating characteristics.
Step motors, or stepper motors, are motors which move in discrete increments. For example, four phase control windings may be provided which can be separately activated in response to inputs from a control system. By addressing the windings in a proper sequence a controllable incremental stepped revolution of the motor shaft is obtained. Thus, step motors are very useful in a control system for positioning mechanical components with a requisite accuracy.
In some instances a number of step motors are used to position component parts of a mechanism. Simultaneous control of the motors typically involves a microprocessor for manipulating data. In some operations a relatively complex computer may be used for the motor control. In other systems, a microprocessor may be associated with each motor for stepping the motor. A central control computer requires complex wiring and a comparatively slow operation is obtained to accommodate the time for data transfer and manipulation with the individual motors. Individual microprocessor applications require relatively complex and expensive control circuits for each motor.
Recent control systems have used programmable array logic circuits (PAL), also known as programmable logic array circuits (PLA), to logically combine selected inputs to obtain outputs for further processing by microprocessor circuitry. For example, U.S. Pat. No. 4,481,569 teaches use of a PAL for bookkeeping signal condition functions ancillary to microprocessor circuitry for controlling robotic servo motors. U.S. Pat. No. 4,509,114 teaches use of a PLA in a control system to interface between an instruction register and primary control circuitry. An operation code in an instruction register is inputted to a PLA to obtain a microword output related to a desired control action. The use of logic arrays taught by the subject patents is in combination with processing circuitry, with a single PAL (PLA) used to obtain a bookkeeping or a translation function.
Available systems for controlling more than one motor generally use a start/stop routine for addressing the motor phases to rotate the motor at an operating speed. Abrupt acceleration and the resulting forces can be significant during the start or the stop of the motor.
Thus, the circuit complexity of conventional systems limits the application of conventional systems to the control of a relatively small number of motors for simultaneous operation. Further, the start/stop characteristics of existing control systems limits the stepping speed for the motors to keep forces within acceptable limits. System operating speed is further limited by the time required for data manipulation and transfer within microprocessor controlled devices.
It is an object of the present invention to simultaneously control a large number of motors.
It is another object of the present invention to program motor acceleration to permit high speed operation without large acceleration forces.
One other object of the present invention is to pipeline data flow and manipulation for improved operating response characteristics.
Yet another object of the present invention is to enable the simultaneous control of a multiplicity of motors, each of which can have individual operating characteristics.
The disadvantages of the prior art are overcome by the present invention, however, and improved method and apparatus are provided for simultaneously controlling a multiplicity of step motors.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.